A retainer wire made of metal to be used in a dentition retaining appliance has been known up to now (hereinafter referred to as "prior art 1"). A retainer wire 10 of the prior art 1 (see FIG. 4), whose end portions both are fixed to the front end of a base part 1, is formed in the shape of a loop and is mounted so as to enclose a plurality of teeth including a corrected tooth (see FIG. 7).
And since a corrected tooth has the retainer wire 10 attached to it in the shape of a loop, even if it attempts to return to the state where it is not corrected, a reactive force is generated in the retainer wire 10 and therefore the corrected tooth is pressed against the base part 1. Since the state of a corrected dentition is kept in this way, it is prevented that the dentition is twisted or inclined similarly to its original state.
In case of a retainer (hereinafter referred to as a "retaining appliance" also) made using a retainer wire 10 of prior art 1 which is composed only of a metal wire, there is a disadvantage that the metal wire comes into a state where it is stuck to the surface of a dentition of front teeth as it is naked and when the mouth is loosened this metal wire results in being seen.
Originally, it is desired for a retainer to be equipped for twenty-four hours, but in many cases a retainer of a metal wire is not continuously equipped because it is not nice to look at, and therefore, a problem is pointed out that since a dentition once corrected% attempts to return to the original state, a period of remedy is made long.
And in order to make a metal wire be along the surface of a dentition, it is necessary to apply a bending process to it using a pair of pliers (pincers).
As a retainer wire capable of solving such a problem, the present inventor has proposed a retainer wire used in a retaining appliance as shown in FIGS. 10 and 11 in Japanese Unexamined Patent Publication No. 213538/1995 (hereinafter referred to as "prior art 2").
A retaining appliance (retainer wire) shown on 10 is composed of a base part 1 which is adapted to the shape of the lower jaw part in the palate and is stuck closely to the reverse surface of a dentition, a holding portion 2b and a spring portion 9a which are made of synthetic resins and are fixed to the front end of the base part 1, and a supporting portion 3 composed of metal wires provided in the left and right rear ends of the base part 1.
Prior to making a retaining appliance, first a model of the lower or upper jaw part in the palate of a patient is made. For example, a model of the lower or upper jaw is made in gypsum, and then a holding portion 2b and a supporting portion 3 are attached onto the said model.
Finally, metal wires are attached to models of the left and right molar teeth to form the supporting portion 3. One end of this wire is also extended at the reverse side of a dentition.
When a holding portion and a supporting portion 3 have been attached to a model of a dentition in such a way, a molten acrylic resin is poured into the model to form a base part 1. When it has been left as it is for several minutes or longer, a retaining appliance in which a saddle-shaped base part 1 has a holding portion 2b and a supporting portion 3 fixed to it can be obtained.
Such a material being resistant to various bacteria or stains in the oral cavity as an acrylic resin is adopted as a material for the base part 1. The thickness of the base part 1 is set at about 0.5 to 1.0 mm.
And as materials for the holding portion 2 and the spring portion 2a, materials which have a thermal contractility and a shape memory due to a heating temperature in the past, are comparatively high in bending strength and in tensile strength, and are resistant to various bacteria or stains in the oral cavity such as polyethylene terephthalate, polybuthylene terephthalate, polycarbonate, copolymer of cyclohexadimethanol-terephthalate and the like are adopted.
As the shape and the size of a holding portion 2, in addition to a circle having a diameter of about 0.5 to 5.0 mm in section, a rectangle or a flat plate having a section of about "(0.3 to 5.0).times.(0.5 to 10.0) mm" is used.
Further, Japanese Unexamined Patent Publication No. 213538/1995 has disclosed a retaining appliance in which a portion 10a adjacent to a spring portion 2a and the other end 10b of a supporting portion 3 are joined to each other by caulking (see FIGS. 5, 6 and 11).
In this way, a retainer wire 10 of prior art 2 uses a transparent plastic resin and in case of a retainer 20 made using this retainer wire 10, since a transparent plastic member is mounted on the surface of a dentition of a front tooth part and the transparent plastic member is only seen even if the mouth is loosened, it is hardly known that the retaining appliance is equipped. Therefore, there is an advantage that since a patient is continuously equipped with it without being concerned about its appearance, the period of remedy is made short.
As a retainer wire of prior art 2 there are two kinds in which one is a retainer wire being made of plastics as a whole (see FIGS. 9 and 10) as described above (since it is made of plastics as a whole, in case that some looseness occurs between a tooth model, and a spring portion 2 and a supporting portion 3, a correcting process to be performed as heating at a high temperature is needed for amendment and the other is a joint-type retainer wire in which only the front tooth part being seen is made of transparent plastics and the part being not seen is made of a conventional metal wire as shown in FIG. 11 (some looseness between a tooth model, and a spring portion 2 and a supporting portion 3 or supporting portion 2c (FIG. 8) can be corrected only by a pair of pliers or the like without heating).
In order to make a metal wire be along the surface of a dentition, it is enough to correct it using a pair of pliers (pincers) or the like, but in order to make a plastic wire, which is a retainer wire of prior art 2 using plastics set by heating, be along the surface of a dentition, it is necessary to heat it at a high temperature and then correct it using a pair of pliers (pincers) or the like.
And in case of making a retainer using a joint-type retainer wire, it is necessary to physically join to each other and use two members which are a plastic portion 2 of a front tooth part (hereinafter referred to as a "holding portion"), and a metal wire of a spring portion 2 and a supporting portion 3.
An object of the present invention is to provide a retainer wire which can solve said problems of a conventional retainer wire and improve the extractive strength of the joint portion of a plastic portion and a metal wire portion.